Facebook said Monday it had closed its acquisition of messaging app WhatsApp, giving the social network a massively popular service for mobile messaging.

The deal, when first announced earlier this year, was to cost Facebook $16 billion plus up to $3 billion in additional Facebook stock options to WhatsApp's founders. Now as of close the deal is worth around $21.8 billion total, based on the higher value of Facebook's stock.

Closure of the deal was announced in a filing with the U.S. Securities and Exchange Commission.

WhatsApp claims to have more than 500 million users worldwide, with fast growth in countries like Brazil, India, Mexico and Russia. Since the initial news of the acquisition, questions have been raised over the extent to which data would be shared between the two companies. WhatsApp says it does not collect names, addresses or email addresses, according to its privacy policy, but it does collect people's mobile phone numbers for the service to work.

Both Facebook and WhatsApp have said that the companies would continue to operate independently. Facebook has said that it would honor WhatsApp's privacy policy, but how exactly any data might be shared going forward is unclear.

The U.S. Federal Trade Commission, while it approved the deal this past April, urged both companies to proceed with caution in how they deal with users' data. If Facebook were to use any of WhatsApp's data in way that's inconsistent with WhatsApp's terms, Facebook would need users' permission first, the agency told both companies.

In a joint statement, both companies said Monday they were "looking forward to connecting even more people around the world, and continuing to create value for the people who use WhatsApp."

A Facebook spokesman did not immediately respond to comment further on the issue of data sharing.

Jan Koum, WhatsApp's founder and CEO, will sit on Facebook's board, the filing said. He will not receive any additional salary or serve on any committees of the board.